Update MSVC portion of README

Include a forgotten object.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Add the progressive GOP flag

This will be needed for properly handling Open GOPs.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Fix handling of case here the first GOP is open

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>